Composition and method to form a self decontaminating surface

ABSTRACT

A method to prepare a self-decontaminating surface, where that method includes dissolving tartaric acid in water, adding titanium (IV) isopropoxide to the tartaric acid solution to form a coating composition in water, and casting that coating composition onto a surface to form a coating having anti-microbial function.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a Continuation-In-Part Application claiming priority to, and thebenefit of, a Non-Provisional U.S. application Ser. No. 13/448,325,filed Apr. 16, 2012, which claims priority to a Provisional U.S.Application Ser. No. 61/476,233, filed Apr. 15, 2011, and a ProvisionalU.S. Application Ser. No. 61/489,630, filed May 24, 2011, which arehereby incorporated by reference herein.

FIELD OF THE INVENTION

Embodiments generally relate a chemical composition and a method to forma self decontaminating surface. In certain embodiments, the chemicalcomposition comprises a photocatalyst. In certain embodiments, thephotocatalyst comprises a titanium oxide moiety.

BACKGROUND OF THE INVENTION

Titanium oxide (e.g., TiO₂) is a nontoxic substance widely used inpaints, paper, plastics, and toothpaste. It is known in the art that analkali hydroxide can be added to an aqueous titanium salt solution toproduce an amorphous titanium peroxide sol. The titanium peroxide solcan be reacted with an aqueous hydrogen peroxide solution to produce anamorphous titanium peroxide sol, which is then heated to hightemperatures to obtain anatase titanium oxide.

Current methods for preparing sheets, coatings, or films comprisingtitanium oxide require that the titanium oxide particles be sintered athigh temperatures (e.g., 200 to 400 degrees Celsius) in order to firmlysupport the titanium oxide on a substrate. Using these prior artmethods, a titanium oxide compound is deposited onto a substrate, andthen baked at approximately 200-400 degrees Celsius to fixedly set thecompound on the substrate. The requirement of such high temperatures tocure the titanium oxide limits its utility, such as use of titaniumdioxide to create self-decontaminating surfaces by retailers orconsumers.

Accordingly, it would be an advance in the art to develop or use a newtitanium oxide sheet, coating, or film deposition.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood from a reading of the followingdetailed description taken in conjunction with the drawings in whichlike reference designators are used to designate like elements, and inwhich:

FIG. 1 is an Atomic Force Microscope image at 50 microns showing acoating on a glass surface, where that coating was formed usingApplicants' composition and method; and

FIG. 2 is an optical image using transmission geometry with 10×objective showing a coating on a glass surface, where that coating wasformed using Applicants' composition and method.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The invention is described in preferred embodiments in the followingdescription with reference to the Figures, in which like numbersrepresent the same or similar elements. Reference throughout thisspecification to “one embodiment,” “an embodiment,” or similar languagemeans that a particular feature, structure, or characteristic describedin connection with the embodiment is included in at least one embodimentof the present invention. Thus, appearances of the phrases “in oneembodiment,” “in an embodiment,” and similar language throughout thisspecification may, but do not necessarily, all refer to the sameembodiment.

The described features, structures, or characteristics of the inventionmay be combined in any suitable manner in one or more embodiments. Inthe following description, numerous specific details are recited toprovide a thorough understanding of embodiments of the invention. Oneskilled in the relevant art will recognize, however, that the inventionmay be practiced without one or more of the specific details, or withother methods, components, materials, and so forth. In other instances,well-known structures, materials, or operations are not shown ordescribed in detail to avoid obscuring aspects of the invention.

Titanium dioxide occurs in nature as well-known minerals rutile, anataseand brookite, and additionally as two high pressure forms, a monoclinicbaddeleyite-like form and an orthorhombic α-PbO2-like form, both foundrecently at the Ries crater in Bavaria. The most common form is rutile,which is also the most stable form. Anatase and brookite both convert torutile upon heating. Rutile, anatase and brookite all contain sixcoordinated titanium.

Titanium dioxide has numerous modifications—in addition to rutile,anatase and brookite there are three metastable forms producedsynthetically (monoclinic, tetragonal and orthorombic), and highpressure forms (α-PbO2-like, baddeleyite-like and cotunnite-like):

Oxidation—loss of electrons or an increase in oxidation state by amolecule, atom or ion. Substances that have the ability to oxidize othersubstances are said to be oxidative or oxidizing and are known asoxidizing agents, oxidants, or oxidizers. Put another way, the oxidantremoves electrons from another substance, and is thus itself reduced.And, because it “accepts” electrons, it is also called an electronacceptor.

In chemistry, photocatalysis is the acceleration of a photoreaction inthe presence of a catalyst. In catalyzed photolysis, light is absorbedby an adsorbed substrate. In photogenerated catalysis, thephotocatalytic activity (PCA) depends on the ability of the catalyst tocreate electron—hole pairs, which generate free radicals (hydroxylradicals: .OH) able to undergo secondary reactions. Its comprehensionhas been made possible ever since the discovery of water electrolysis bymeans of the titanium dioxide. Commercial application of the process iscalled Advanced Oxidation Process (AOP). There are several methods ofachieving AOP's, that can but do not necessarily involve TiO₂ or eventhe use of UV light. Generally the defining factor is the production anduse of the hydroxyl radical.

When TiO₂ is illuminated with light of sufficient energy, electron-holepairs are excited so that additional electrons go across the band gap toconduction band (“CB”), while holes stay in the valence band (“VB”). Theexcited electrons may then be used for redox reactions at the surface ofTiO₂. There are multiple phases of TiO₂. For example, Rutile phase canbe excited by visible light, but has a fast charge recombination rate;Anatase, on the other hand, has a slow recombination rate, but can onlybe excited by UV lights. Thus, it is reasonable to produce mixed phasephotocatalyst to increase the total efficiency

Certain titanium oxide crystalline morphologies exhibit photocatalyticcharacteristics when exposed to Ultra Violet (UV) light. When exposed toUV light, titanium oxide, creates electron-hole pairs which generatefree radical (e.g., hydroxyl radicals). The degree of photocatalyticstrength varies depending on the type of titanium oxide, for exampleanatase titanium oxide (particle size of about 5 to 30 nanometers) is astronger photocatalyst than rutile titanium oxide (particle size ofabout 0.5 to 1 microns). Therefore, titanium oxide has potential use insterilization, sanitation, and remediation applications.

In certain embodiments, Applicants' method and composition provide atitanium alkoxide starting material (RO)₄Ti photocatalyst surfacecoating precursor. For example, in certain embodiments Applicants'method forms a liquid coating composition using titaniumtetraisopropoxide 1.

In certain embodiments, that liquid coating composition is cast onto asurface to form a coating comprising a linear polymeric structure 3 onthe surface.

In other embodiments, Applicants' method forms a liquid coatingcomposition using titanium tetraisopropoxide 2, and casts that coatingcomposition solution onto a surface to form a coating comprising across-linked structure 4 on the surface.

In other embodiments, Applicants' coating composition is formed usingtitanium tetraisopropoxide

The following Example is presented to further illustrate to personsskilled in the art how to make and use the invention. This example isnot intended as a limitation, however, upon the scope of the invention.

EXAMPLE

9.0 grams of tartaric acid were dissolved in 0.120 liters of water in anErlynmeyer flask to give a 0.5 molar solution. This solution was stirredovernight at room temperature. The following day, the tartaric acidsolution was filtered through filter paper (Whatman #1), thensubsequently through a 0.2 micron PRFW filter to remove particulates. 25mL of filtered 0.5 M tartaric acid (0.01249 moles of tartaric acid) waspoured into a round bottom flask and chilled on ice with stirring. 3.69grams of titanium (IV) isopropoxide was added slowly first with a 1 mLaddition. 1 mL aliquots of titanium (IV) isopropoxide were added untilall of it was added to the tartaric acid solution.

Upon addition of the titanium (IV) isopropoxide the ice bath wasremoved. The solution remained a solution for approximately 10 minutesafter which it became a clear gel and became progressively opaque(white). The gel was stirred at RT overnight. The gelatinous materialwas mixed with water, or alcohol ROH and water, and then cast onto aglass slide to form a coating thereon.

Depending on the stoichiometry of the starting materials, in certainembodiments Applicants' coating of this Example comprises a tartaricacid/titanium isopropoxide adduct 5, wherein R is H, alkyl, and phenyl.When the molar ratio of TI(OR)₄ and tartaric acid is greater that about3, the adduct product 5 predominates.

When the molar ratio of TI(OR)₄ and tartaric acid is about 1, Apolymeric product 6 predominates, wherein (r) is between 2 and about 10.When the molar ratio of TI(OR)₄ and tartaric acid is greater than 1 butless than about 3, a mixture of adduct 5 and polymer 6 is obtained. Inthe Example, the molar ratio is about 5, and adduct 5 is predominatelyformed.

In other embodiments, Applicants' coating composition comprises one ormore hydroxyl acids other than tartaric acid in combination with TiO₂.In certain embodiments, these one or more hydroxyl acids include one ormore alpha hydroxyl acids including glycolic acid, lactic acid, citricacid, and/or mandelic acid. In certain embodiments, these one or morehydroxyl acids include one or more beta hydroxyl acids includingsalicyclic acid and/or beta-hydroxypropionic acid.

FIGS. 1 and 2 show images of the coating formed on the glass surface.FIG. 1 is an Atomic Force Microscope image at 50 microns. FIG. 2 is anoptical image using transmission geometry with 10× objective.

In certain embodiments, Applicants' coating composition is embodied in aflexible, planar member to form a composite disinfecting wipe.Applicants' composite disinfecting wipe is capable of cleaning andremoving residues from soiled surfaces while simultaneously destroyingundesirable microorganisms, e.g. bacteria, mold, viruses, prions and thelike that colonize on common surfaces with which people come intocontact, such as doorknobs, countertops, toilet seats, floors, beds,walls, and the like.

Glass slides prepared in accord with the Example were inoculated withbacteria or virus and sampled at various times with a sterile cottonswab. That cotton swab was placed into a tube containing a neutralizingbroth. Methicillin resistant Staphylococcus aureus (“MRSA”) and MS-2were utilized. MS-2 is a bacteriophage used as a surrogate forNorovirus, Enterovirus, Polio, and the like. TABLE 1 recites logreduction of MRSA-inoculated glass slides coated using various weightpercent solutions of the composition of the Example to form a coating onthe glass slides prior to MRSA inoculation.

TABLE 1 Log Reductions of MRSA Using Composition Of Example 10% 5% ~3%~1% Time Points Log Reduction 10 minutes 1.0 0.9 0.4 0.3  1 Hour NotDone Not Done >5.9 0.1  2 hours >5.6 >4.0 >5.5 1.8

TABLE 2 recites data using slides coated using a 10 weight percentcomposition of the Example to form a coating on the glass slides priorto either MRSA or MS-2 inoculation. MS-2 was showed an average of 2.4log reduction at two hours. MRSA showed greater than a 5.6 log reductionat two hours.

TABLE 2 Average Log Reduction For MRSA And MS-2 At Two Hours 10 MINUTES2 HOURS MS-2 0.6 2.4 MRSA 1.9 >5.6

A test using glass slides coated using a 3 weight percent solution ofthe coating composition of the Example, and inoculated with either MRSAor MS-2. wherein the slides were inoculated in the dark, did not showany log reduction. This result shows that the titanium moieties in theglass slide coating were providing anti-microbial function via aphotocatalytic effect.

TABLE 3 recites data regarding the anti-microbial efficacy of coatingsformed on glass slides using various weight percent solutions of thecoating composition of the Example.

TABLE 3 Log Reductions Of Organisms After 1 Hour 5% ~3% ~1% Organism LogReduction MS-2 4.1 1.3 1.7 E. coli >5.0 >5.0 >5.0 Ps.aeruginosa >5.2 >5.2 >5.2

While the preferred embodiments of the present invention have beenillustrated in detail, it should be apparent that modifications andadaptations to those embodiments may occur to one skilled in the artwithout departing from the scope of the present invention as set forthherein.

We claim:
 1. A coating disposed on a surface, formed by the methodconsisting of: dissolving tartaric acid in water; forming an opaque gelby adding titanium (IV) isopropoxide to said tartaric acid solution toform an 18 weight percent loading of tartaric acid and titanium (IV)isopropoxide in water; diluting said gel with water to form a 10 weightpercent loading of tartaric acid and titanium (IV) isopropoxide inwater; casting said 10 weight percent aqueous gel onto a surface to forma coating; inoculating said surface with MRSA bacteria, wherein: saidinoculated surface comprises an initial MRSA concentration; saidinoculated surface shows greater than a log 5.6 reduction in MRSAconcentration after 2 hours.
 2. A coating disposed on a surface, formedby: dissolving tartaric acid in water; forming an opaque gel by addingtitanium (IV) isopropoxide to said tartaric acid solution to form an 18weight percent loading of tartaric acid and titanium (IV) isopropoxidein water; diluting said gel with water to form a 3 weight percentloading of tartaric acid and titanium (IV) isopropoxide in water;casting said 3 weight percent aqueous gel onto a surface to form acoating; inoculating said surface with MRSA bacteria, wherein: saidinoculated surface comprises an initial MRSA concentration; and saidinoculated surface shows a greater than log 5.5 reduction in MRSAconcentration after 2 hours.
 3. A coating disposed on a surface, formedby: dissolving tartaric acid in water; forming an opaque gel by addingtitanium (IV) isopropoxide to said tartaric acid solution to form an 18weight percent loading of tartaric acid and titanium (IV) isopropoxidein water; diluting said gel with water to form a 1 weight percentloading of tartaric acid and titanium (IV) isopropoxide in water;casting said 1 weight percent aqueous gel onto a surface to form acoating; inoculating said surface with MRSA bacteria, wherein: saidinoculated surface comprises an initial MRSA concentration; and saidinoculated surface shows a log 1.8 reduction in MRSA concentration after2 hours.